GB2042215A - High speed process and apparatus for painting metal strapping - Google Patents

Abstract

Process and apparatus for high speed painting of metal strap includes means for applying a thin layer of paint to the strap and a paint dryer through which the strap is subsequently passed. The dryer has opposing banks of infrared radiation emitters with control means to vary the intensity of the radiation, responsive to the linear speed of the strap to provide the required intensity to achieve a desired strap temperature at which the paint is dried. The controller is adapted to immediately drop the intensity when strap movement is stopped to provide a substantially lowered strap temperature to preclude harming paint finish. <IMAGE>

Description

SPECIFICATION High speed process and apparatus for painting metal strapping This invention relates to high speed process and apparatus for producing painted metal strap using infra-red radiation as the means for drying freshly painted strap. The metal strap may be of the type used to bind carton, boxes, cargo and the like.

It is common to paint strapping to protect it from the elements. It can be painted by passing it through a paint bath, allowing it to dry in a heated forced-air convection type drying tower and coiled with the option of waxing the painted strap prior to coiling.

Such technique is disclosed in Canadian patent 661,066 issued April 9, 1963 to Sharon Steel Corporation. The method of painting strap in this manner is satisfactory for the very slow line speeds of that unit.

More expedient forms of strap painting are known wherein metered rolls are used to roll paint onto the strap and then use forced-air furnace to dry the strap. The use of metered rollers have their drawbacks because at speeds in excess of approximately 250 feet per minute, they do not apply a constant thickness of paint film to the strap. A further drawback, which is inherent in most prior art strap painting systems, is the use of expensive accumulators which accumulate strapping to permit continuous run of the linethroughtthe painting and drying units while new metal sheet material is being loaded onto payoff reels, or coiled painted strap is taken from the coiling apparatus.The accumulators are necessary because the bulky expensive to operate forced-air convection type drying units, the heating of which is usually supplied by gas-fired furnaces, cannot decrease their temperature rapidly to a level at which the paint would be unharmed if the strap stood still in drying chambers. The accumulators, therefore, ensure a continuous movement of painted strap through the system. A further drawback in the use of the gas-fired furnaces is that they do not readily respond to change in line speed.

In some instances, it requires hours to vary in a controlled manner the temperature within the tower so that it is hopeless to attempt temperature variation determined by varying line speed.

There are infrared heater units which have been used to dry inks and paints, such as the high intensity infrared heaters manufactured and sold by Research Inc. of Minneapolis, Minnesota, United States of America. Such heaters have been used, for example to dry a layer of paint on particle boards which are passed in a horizontal plane through a horizontally-oriented heater unit. The paint is applied to the board by wheel-type coaters. Such apparatus, however, does not lend itself to high speed painting.

A drawback of the prior art is the inability to provide a drying chamber which can immediately respond to varying line speeds and accomplish drying of the freshly painted strap in limited space and with minimum energy usage.

According to one aspect of the invention there is provided an apparatus for high speed painting of metal strap having a thickness from 10 to 50 thousanths of an inch (24 to 120 thousanths of a centimetre) comprising means for applying a thin layer of paint on such strap, a paint dryer having opposing banks of electrically powered high intensity shortwave infrared radiation emitter lamps, a roller device for passing such strap through said dryer between said emitter banks and out of said dryer, means for measuring the linear speed of such strap, controller means for varying the electrical power to said lamps to thereby immediately vary the intensity of such radiation, said speed measuring means being adapted to signal said controller of measured strap linear speed and said controller being adapted to control electrical power to said lamps to provide the required radiation intensity to achieve for measured line speed a desired strap temperature at which such paint is dried, and said controller being adapted to vary immediately electrical power to said lamps responsive to measured strap linear speed change, fans means for providing a flow of air between said emitter banks and over such strap and out the dryer, said controller means being adapted to immediately drop the radiation intensity when strap movement is stopped to provide a substantially lowered strap temperature to preclude harming paint finish, said roller device including at least one refrigerated roller at the dryer exit over which said strap passes, the at least one roller being refrigerated sufficiently to reduce strap temperature to a level at which such paint is tack free and coiling means for coiling cooled painted strap.

According to another aspect of the invention there is provided a method for painting metal strap at linear speeds as high as in the range of 1,000 feet (28,800 centimetres) per minute comprising applying a thin layer of paint on said strap which has a thickness ranging from 10 to 50 thousanths of an inch (24to 120thousanths of a centimetre), passing such freshly painted strap between opposing banks of electrically powered high intensity shortwave infrared radiation emitter lamps to heat with such infrared radiation such strap to temperatures which dries such paint, providing a stream of air between said banks and over such strap and exhausting such air at the end of the emitter banks, constantly measuring the linear speed of such strap, controlling the electrical power to said lamps to achieve a desired strap temperature on exiting from the emitter banks for a measured linear strap speed and immediately varying the electrical power to said lamps to vary the intensity of said radiation in response to a measured change in such strap linear speed and when strap movement is stopped, immediately dropping the intensity of radiation to provide a reduced strap temperature to maintain in such stream of air a satisfactory strap paint coating, chilling such strap as it exits such emitter banks and coiling the painted strap.

A process and apparatus embodying the invention are capable of painting strap and drying the freshly painted strap at high linear speeds of up to 1,000 feet (28,800 centimetres) per minute or more by drying such painted strap in a field of infrared radiation at very high line speeds.

It is an advantage of one embodiment of this invention, to control the radiation intensity in a manner to respond almost immediately to line speed changes to always ensure painted strap quality even during starting and stopping of the iine.

It is another advantage of another embodiment of this invention to paint strap at such high speeds using equipment with substantially less energy requirements, less manufacturing space requirements, and substantially less capital equipment costs compared to the former forced-air oil or gas-fired forms of paint dryers.

It is another advantage, according to a further embodiment of the invention, to electro-deposit a fairly consistent thickness of paint on the strap over varying line speeds to economize on quantity of paint used.

One preferred embodiment of an apparatus, according to this invention, for the high speed painting of metal strap includes means for applying a thin layer of paint on the strap and a paint dryer.

The thickness of the strap in in the range from 10 to 50 thousanths of an inch 124 to 120 thousanths of a centimetre). The dryer has opposing banks of electrically powered high intensity shortwave infrared radiation emitter lamps. A roller arrangement is provided to direct the freshly painted strap through the paint dryer between the banks of emitters.

Means is provided to measure the linear speed of such strap. Control means varies the intensity of the infrared radiation by varying the electrical powerto said lamps responsive to meansured changes in the linear speed of the strap, to provide the required radiation intensity to achieve for measured strap speed a desired strap temperature at which such paint is dried. Fan means directs a flow of air between the emitter banks and over the strap and out of the drier. The controller is adapted to immediately drop the radiation intensity when strap movement is stopped to provide a substantially lowered strap temperature to preclude harming the paint finish. In the roller arrangement, one or more refrigerated rollers is provided at the dryer exit to reduce the strap temperature to a level at which the paint is tack free.The strap may be further cooled before coiling and preparation for shipping.

One preferred embodiment of a process, according to this invention, to accomplish the high speed painting of the metal strap comprises applying a thin layer of paint on the metal strap, passing the freshly painted metal strap between opposing vertically extending banks of electrically powered high intensive, shortwave infrared emitter lamps to heat the strap to temperatures which dry the paint. A stream of air is directed between the emitter banks and over the strap and is exhausted at the end of the emitter banks. The intensity of the radiation is controlled to vary immediately the intensity of the radiation by varying the electrical power to the lamps responsive to a measured change in strap linear speed to achieve the desired strap temperature on exiting from the emitter banks for measured linear strap speeds.When the strap movement is stopped, the intensity of radiation is immediately dropped to provide a reduced strap temperature to maintain in such stream of air a satisfactory strap paint coating.

The strap is chilled on exiting the emitter banks and optionally further cooled before coiling.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic elevation view of an apparatus for slitting metal sheet into strap, painting the strap, drying the strap, cooling, waxing and recoiling the strap; Figure la is a continuation of the system shown in Figure 1; Figure 2 is an isometric view of an electrodeposition tank for applying paint to the strap and of the lower portion of the drying tower; Figure 3 shows a refrigerated bath for cooling the dried painted strap and for waxing the so-cooled strap; Figure 4 is a block diagram representative of controllers used to control the electro-deposition tank and the intensity of the infrared radiation; and Figure 5 is a schematic of further details of the controller for the infrared radiation emitters.

Figure lisa schematic representation of the system for applying and drying or baking paint on strapping. The dryer for baking the paint by removing solvents from and heating the paint is in the vertical position. It is understood, of course, that with certain building height restrictions and other space limitations that the dryer may be sloped or positioned in a horizontal plane. However, the preferred system is that shown because, as can be appreciated, with the dryer vertical, a relatively simple roller arrangement may be devised to pass the painted strap directly upwardly into the drying tower.

Referring to Figure 1,the strapping 10 is passed through a paint applying device 12 and dried in tower 14. The strap 10 is formed by slitter device 16, slitting sheet metal or broad strap 22 paid-off from roll 20 by payoff reel 18. From the slitter wheels 24, the plurality of straps are directed into upper and lower levers 10a, Ob, where opposing rollers 26 of the deburring device debug the edges of the spacedapart strap. Roller 28, in connection with roller 30, recombines the stream 1 ova and 10b of straps to provide essentially co-planar straps passing over roller 30 in preparation for travel into the paint applying device 12.

A roller arrangement comprises rollers 32, 34 and 36 which determine in part the path of the strap upwardly through the drying tower 14. The strap is passed downwardly alongside the tower into a refrigerated bath 38 under refrigerated roller 40 preparatory to waxing of the strap in tank 42. The so-treated strap is then passed in direction of arrow 40 and recoiled on recoiler apparatus 46 on power driven spoolers 48 and 50. The incoming several strands are divided and spooled on the several spool channels defined by movable plates on spoolers 48 and 50.

Aside from pay-out reel 18 at the start of the line, a further pay-out reel 18a has roll 20a of sheet metal.

On coming to the end of roll 20, the beginning of roll 20a is butt welded to the end of sheet 22 of roll 20. To accomplish the butt joint, an in-line butt joint welder and weld stress relieve unit 54 are used. The end of sheet 22 and the beginning of sheet 22a are sheared to provide parallel surfaces for butt welding in welder unit 58. The welder may be the common known Tig (Trademark) welder. After formation of the butt joint weld, the line is moved slightly to place the joint under weld stress-reliever 60 which relieves the stress of the joint weld. For standard duty strap, the stress relieved joint may remain in the strap. This eliminates the need to cut the joint out of the strap.

However, for heavy-duty of high-tensile strength strapping, regulatory bodies require that the welded joint be removed from the strap. This necessitates stopping the line. This stoppage of the line occurs when taking material off spoolers 48 and 50 or joining new material at welder 54. This leaves the freshly painted strap standing still in the drying tower. As explained with respect to the background, it is common to use accumulators to compensate for this, so that strap is continuously moved through the tower. However, with this invention, one is able to shut the line down to accomplish all of the above operations without causing any harm to the painted strap standing in the tower and on start-up ensure a properly dried paint, so that all strap is usable.

Although various techniques may be employed to applying paint to the strap, it has been found that electro-deposition of paint onto the strap is a preferable technique at high line speeds. As shown in Figure 1, an electro-deposition device 12 consists of tank 62 containing paint emulsion 64 formulated for use in the electro-depositing process. Rollers 30, 32 and 34 determine the path of the strapping downwardly and upwardly throught the electrodeposition tank 62. As schematically shown, roller 30 is charged by spring-loaded followers 66 and the paint in the area of the upstream portion of the strap is oppositely charged by opposing plates 68 via electrical leads 70. The voltage applied to plates 68 determines the potential difference between the paint and the strap to apply a particular thickness of paint to the oppositely charged strap.

After electro-depositing a layer of paint on the strap 10, they are passed upwardly through the drying tower 14 between opposing vertically extending banks 72 and 74 of infrared radiation emitters.

For the high line speeds, a preferred type of infrared emitters is a high intensity type. Each bank, therefore, consists of a plurality of spaced-apart horizontally extending lamps 76 which, when powered, emit high intesity infrared radiation. The lamps may be of the tungsten filament-quartz body type. The infrared radiation is shortwave of a wave length of 76 to 5 microns. With the tungsten-quartz lamp the energy distribution reaches a peak energy at approximately 1.15 microns. The shortwave infrared radiation is transmitted directly to the strap without heating the surrounding air. The shortwave infrared radiation quickly penetrates the strap to heat it from the inside out so that the strap temperature is raised to a level which is sufficient to dry the paint.Therefore, as the strap is moving upwardly through the tower41 at high speeds up to 1,000 feet (28,800 centimetres) per minute or more, the strap is exposed to the radiation where the intensity of the radiation is controlled to ensure that the strap, on reaching the upper level of the tower 14, is at a temperature sufficient to have dried or baked the paint, but of course, not so high as to cause any paint damage before the strap is cooled.

A distinct advantage in using electro-deposited paint, which may be of an acrylic water-based emulsion, is that the water driven from the strap during the drying process may be axhausted from the tower to atmosphere without any need for solvent recovery. It is of course, understood that other types of paints may be used which may be electro-deposited or applied by other means. Such paints include polyester based paints.

It has been found that, for some types of electrodeposited paint, a strap temperature of approximately 300"F on exiting the tower is required to achieve satisfactory paint baking. At this temperature, all of the solvents may have been driven from the paint; however, the paint at this temperature is still in its thermoplastic state, so that it is very tacky.

The rollers 34 and 36 are designed to prevent substantial amounts of paint sticking to them. One approach in avoiding paint adherence is to coat the rollers with polytetrafluoroethylene. The polytetrafluoroethylene coated rollers also serve the useful purpose of allowing the straps to slip over the rollers relative to each other. This is particularly advantageous during line start-up where it is desired to take up slack in one or more of the straps as they stand in their vertical position in the tower. The slack can be easily taken up by pulling the slack strap at the rewinderto bring it into line with the others.

The rollers are refrigerated where refrigerant passes into the rollers through inlets 78 and is carried away by outlets 80. The purpose of the refrigerant is to chill the rollers sufficiently so that, as the strap leaves roller 36, the paint has been sufficiently cooled to provide a tack free or essentially tack free painted strap surface. Another approach to reduce paint adherence to the roller when narrow strap is used is to provide Vee-shaped grooves in the roller surface. The narrow straps, therefore, sit with their edges contacting sides of each Vee-shaped groove. This results in disturbing the paint at the edges of the strap which is satisfactory for most commercial uses. Cooling of the strap, when Veeshaped rollers are used, is accomplished in refrigerated bath 38 at the tower base.

The so-painted strap may be preferably waxed before coiling. To ensure the strap is below the boiling temperature of the wax in the waxing device 42, the strap is optionally passed through refrigerated bath 38 underneath roller 40. Roller 40 may also be refrigerated by refrigerant in lines 82 and 84. This refrigeration ensures that the strap on entering the wax bath 86, is at a temperature below the boiling point of the wax. A wax film is applied to the strap as it travels through the bath under roller 88. The strap 10, as it emerges from the wax bath, passes over rollers 90 and 92, intermediate of which is a wax wipe arrangement 94 which removes excess wax from the strap. The so-waxed strap is recoiled on spoolers 48 and 50. The power driven spoolers provide the pull for moving the strap through the apparatus.With the ability of this system to start and stop at will, it is only necessary to provide the minimum number of spoolers needed, depending upon the number of straps to be treated by the system. No duplication of spoolers is required as in other systems using accumulators.

Afan with ducting 96 may be provided to define an air flow in the direction of arrows 98 which pass through ports 124 in the ceramic backing of the tungsten-quartz lamps 76 to provide a central air stream 102. The flow is upward between the lamp banks 72,74 and exhausted out the top of the tower in the direction of arrow 104. An exhaust fan 105 is provided at the top of the tower to withdraw the air and exhaust to atmosphere. Such airflow serves in cooling the lamps and ceramic backing and exhausting fumes and water vapour from the tower to expedite the drying of paint on the strap. The infrared radiaton heating is not affected by the flow of air through the tower, because the heating effect is based on the metal strap absorbing the transmitted radiation and converting this into heat energy.

At the base of the tower, diagonally-oriented, spaced-apart shields 106 are provided on each side of the strap 10 to shield radiation from the electrodeposition tank 62 and to shield the wipes 108 provided above the tank which serve to wipe excess water from the strap. It is important to shield the wipes from such radiation since excess heating of the wipes dries them out and results in marring the paintfinish.

Turning to Figure 2, it can be seen that the strap 10, as it passes over gathering roller 28, is passed over roller 30 which includes a plurality of channels 110 to define guideways for the strap 10. Similarly, roller 32 has similar channels 112 to guide the strap as it passes through the paint bath to ensure even spacing and non-overlapping of the strap during paint application. Roller 34 at the top of the tower is provided with similar channels to ensure that the several strands of strapping 10, in passing through the tower, are evenly spaced-apart and are not permitted to overlap. This ensures a uniform heating of the strap in the radiation field to achieve proper drying of the paint prior to strap exit. All of the rollers are, of course, mounted on bearings, such as 114 for roller 30 so that they are freely rotatable.

The relationship of the charged plates 68 is shown in somewhat more detail in Figure 2. The strapping passes between the charged plates and has applied thereto by electrical attraction a layer of paint.

Prior to the plurality of strap entering the drying tower 14,they pass through opposing wipes 108.

The wipes, according to a preferred embodiment, are made up of two opposing pieces of compressible sponge mounted on support members 116 and 118.

The plates 116 and 118 are movable towards and away from one another. The foam pads are compressed by using turn buckles to achieve the desired degree of pad compression. The electro-deposition process causes the paint particles to adhere to the strap surface. The water used in the system is deionized and has a resistance of at least 100,000 ohms. A substantial amount of water, due to its surface tension, adheres to the strap as it is moving at these high speeds of up to 1,00 feet (28,800 centimetres) per minute or more. The wipes, therefore serve to strip or wipe this surface water off of the paint-coated strap. The water drips back into the electro-deposition bath. It has been found that sponge in a particularly suitable material to achieve this wiping action, in that the sponge is compressible to surround the strap and apply a modest pressure thereto in achieving the wiping action.

Aside from sponge, other types of wipes may be used, such as felt pads, rubber squeegees and the like, depending upon line speeds, the characteristics of the paint being used and the type of wipe compression. The relationship of the radiation deflection plates 106 relative to the wipes are shown which, as mentioned, protect the wipes from drying out.

Further details of the air flow ducting are shown in Figure 2. Afan is placed at the base of ducting 122.

Communicating with duct 122, are lateral ducts 96 which, as explained with respect to Figure 1, are in communication with the space between the banks 72,74via ports 124 to provide the central stream of air 102. Auxillary ducts 126 are provided on each side of the central area of the tower and auxillary fans pass air through these ducts 126 at entrance 127. Several entrances for each duct 126 are provided to ensure sufficient air flow. These provide cooling air flowing upwardly and exhausted atthe top to cool the lamp tips or electrodes 128 which project through the ceramic backing material 130.

Such cooling is needed in high speed applications where the power requirements are fairly large. This avoids overheating of the lamp electrical connect terminals and precludes lamp burn-out.

Subsequent to drying the painted strap and chilling by rollers 34 and 36, the strap is passed downwardly in the direction of arrow 132 into refrigerated bath 38 under roller 40 in the manner shown in Figure 3. As mentioned, refrigerant is supplied to roller 40 via lines 82,84 and similarly the water in bath 38 is refrigerated to maintain a sufficiently low temperature to ensure cooling of the strap to a level below the boiling point of the wax bath 42. As shown, roller 40 includes channels 134 which ensure proper relative alignment of the strap 10. To prevent water from entering the wax bath, a wipe arrangement 136 is provided to wipe off the strapping prior to wax bath entry over tensioning roller 38. The strap passes under roller 88, immersed in the molten wax bath and passed upwardly over roller 90 through a wax wipe system 94. The pressure exerted on the opposing pads of the wax wipe system may be controlled by hydraulic or pneumatic cylinders generally designated 140. They maintain sufficient pressure on the wipes to ensure that no excess wax remains on the strap upon exiting the waxing system and priorto recoiling. As can be appreciated, the purpose of waxing the strap is to facilitate use of the strap in binding bulk loads or cartons.

Referring to Figure 4, as shown in block diagram, there are controllers for the electro-deposition paint tank and for the high intensity infrared lamps in the tower. The input to the controllers for adjusting lamp intensity and potential applied to the paint tank is provided by a tachometer 142 which is connected to the slitter device 16. The signal in line 144 from tachometer 142 is proportional to the line speed. For example, the output from tachometer 142 may be a D.C. voltage representative of the speed measured by the tachometer. The signal in line 144 is fed to both controllers by split lines 146 and 148. The controller 150 for the tower is programmed in receiving a signal in line 148 to provide a predetermined voltage in line 152 to power the lamps to achieve the proper radiation intensity for a particular line speed.Similarly controller 154 receives the signal from line 146 and may be preferably programmed to provide a predetermined voltage in line 156 to achieve the desired potential defference between electrodes 68 and ground 66 to apply the desired thickness of paint to the strap for a particular line speed.

The details of installing the process controller for the drying tower are shown in Figure 5. The controller 150 has peripheral inputs from manual adjustment input network 158 and automatic input network 160 which receives tachometer signal in line 146. The power to the controller 150 is supplied at terminals 162 through fuses 164. The power may be of the magnitude of approximately 570 volts, three phase 60 hertz cycle. Power from the controller 150 is derived to run fan motor 166 which drives the fan to supply air to the base of the duct work 122, shown in Figure 2, and to run fan motor 168 which drives fan 105 to withdraw air from the tower in the direction of arrow 104. Power from the controller 150 is also derived at terminals 170 to power the lamps which have been set up in a delta-load configuration.

Either bank 72 or 74 for the lamps, therefore, consists of three sets 172. Another set of outputs would provide power to the other bank of lamps.

Current sensors 174 in the form oftoroidal cores are provided to sense the current in lines supplying terminals 170. A volt meter 176 is provided to display the sensed voltage powering lines leading to terminals 170.

The manual adjustment for the output of the controller 150 at terminals 170 is determined by network 158. The double pole-double throw switch 180 is shown in the manual output adjustment position. The setting of potentiometer 178 provides input to controller 150 via lines 181, 182. When the switch 180 is in the automatic position, then input is derived from tachometer signal in line 46 through resistor net work 160 to provide an input signal to controller 150 via lines 186 and 188.The controller 150, in detecting an input from either the manual or automatic adjustment, provides according to its programme the necessary power at terminals 170 to provide the radiation intensity needed to heatthe strap to the desired temperature for the particular line speed.

When the controller is on the automatic setting and the line is stopped, and "idle" input is provided by potentiometer 190. The controller uses this input when it no longer receives input from lines 186,188 to determine the reduced power at terminals 170, so that the intensity of radiation is lowered to a level which does not harm the paint finish. In providing this "idle" setting for the lamps, it ensures on restart of the system, that the lamps are reactivated immediately to ensure radiation intensity is at the level needed to give the desired strap temperature for drying the paint before the strap exits the tower.

The set-up of the controller 150 is determined initially by trial and error. Various voltages must be determined for varying line speeds and various strap thicknesses so that adjustments can be made in the potentiometers of the tachometer input and manual input to achieve the desired results. On the manual setting for switch 180, the power to terminals 170 can be varied by adjusting potentiometer 178. For a line speed of 500 feet per minute, the potentiometer 178 may be varied to provide a voltage to the loads 172 which gives the desired intensity to provide a baked painted strap exiting the tower. The voltage to the loads is displayed by voltmeter 176.On switching over to automatic, the input from tachometer 146 may be adjusted by the potentiometer 161 of network 160 to provide an input signal to the controller which results in a voltage output shown on volt-meter 176, the same as output previously provided by potentiometer 178.

The controller 150 may be programmed to increase or decrease automatically the voltage output for varying speeds to provide outputs which achieve paint drying at various strap linear speeds.

The controller 150 may be adjusted to ensure that the power at terminals 170 is reduced to the "idle" temperature as set in potentiometer 190 almost instantaneously or immediately on receiving input signal in line 146 that the line is stopped. Similarly, when there is an input signal from line 146 to indicate that the line is restarted, the controller 150 may be adjusted to ensure immediate response in terminals 170 to activate the loads 172 to give the desired intensity which dries or bakes the paint prior to the strap leaving the tower. This immediate response in the controller 150 is vary advantageous due to the start/stop nature of the line with respect to adding new material to the line or taking off coiled painted material.Such start/stop in the system obviates the need for accumulators and rewinders which are very costly, space consuming and can only accommodate so much down time on either end of the line.

The controller 154 for the paint tank 12 may function in a manner to vary the potential on the electrode 68 in response to variation in line speed. It is understood that it may not be necessary to vary the voltage of the electro-deposition paint tank with variation in line speed if variations in applied paint thicknesses can be accommodated. However in some instances, it is desirable to vary the voltage applied to the tank in response to change in line speed. For example, as the line speed increases, the voltage may be proportionally increased by controller 154 to apply the same thickness of paint to the faster moving strap. Conversely, as the strap speed slows down, the voltage may be decreased by controller 154 to apply the same paint thickness to the slower moving strap.In other words, for a particular line speed, a particular potential is applied to the electrodes to attract a predetermined thickness of paint to the strap. The variation in potential on the electrodes 68, for variation in line speed, results in a fairly constant layer application of paint to the strap.

As mentioned, the dryer having the infrared heaters or emitters may be sloped or horizontally positioned. It can be gathered from the description of the preferred embodiments that mechanical devices, such as tension bridles, would be necessary to maintain proper strap tension so that, when passing through the tower, it is not permitted to contact the lamps. In addition, protector bars may be provided in the dryer to prevent a sagging strap from touching the lamps. In using such tension bridle, it would of course, be necessary to position it upstream of the paint applying device so that the freshly painted strap can be passed to the tower by a roller which would provide minimal engagement with the strap.

Such roller may be the same as the Vee-shaped roller which would only contact the strap edges.

The system may be used for painting various thicknesses and widths of strap preferably in the range of 10 to 50 thousanths of an inch thick. The width may, of course vary considerably depending on its end use. As mentioned, with respect to the controller, the amount of power needed to dry the strap is dependent upon the strap thickness because in the use of infrared radiation, the baking aspect is accomplished by heating the strap from the inside out. Therefore, a thicker strap requires higher radiation intensity to properly bake the freshly painted strap.

The process and apparatus, according to this invention, therefore, provides an energy efficient system for painting strap at speeds in excess of 250 feet per minute and up to 1,000 feet per minute or more. Such higher speeds of painting have not been achieved in any existing unit due to the inability to apply paint to strapping at these speeds and dry the strapping in a unit which is of the small size and has the ability to operate in an instant startistop manner.

Claims (24)

1. Apparatus for high speed painting of metal strap having a thickness from 10 to 50 thousanths of an inch (244 to 120 thousanths of a centimetre) comprising means for applying a thin layer of paint on such strap, a paint dryer having opposing banks of electrically powered high intensity shortwave infrared radiation emitter lamps, a roller device for passing such strap through said dryer between said emitter banks and out of said dryer, means for measuring the linear speed of such strap, controller means for varying the electrical power to said lamps to thereby immediately vary the intensity of such radiation, said speed measuring means being adapted to signal said controller of measured strap linear speed and said controller being adapted to control electrical power to to said lamps to provide the required radiation intensity to achieve for measured line speed a desired strap temperature at which such paint is dried, and said controller being adapted to vary immediately electrical power to said lamps responsive to a measured strap linear speed change, fans means for providing a flow of air between said emitter banks and over such strap and out the dryer, said controller means being adapted to immediately drop the radiation intensity when strap movement is stopped to provide a substantially lowered strap temperature to preclude harming paint finish, said roller device including at least one refrigerated roller at the dryer exit over which said strap passes, the at least one roller being refrigerated sufficiently to reduce strap temperature to a level at which such paint is tack free and coiling means for coiling cooled painted strap.

2. An apparatus as claimed in Claim 1, wherein said dryer is a vertical paint drying tower, said tower being located above said paint means, said roller device passing such strap upwardly from said paint means between said emitter banks, and out the tower top.

3. An apparatus as claimed in Claim 2, wherein there are two adjacent refrigerated polytetrofluoroethylene coated rollers from which such strap is trained downwardly beside said tower into a refrigerated bath preparatory to strap waxing, means for applying a thin layer of wax to such cooled strap prior to its being coiled.

4. As apparatus as claimed in Claim 3, wherein said means for applying wax comprising a molten wax bath through which the strap is trained and a pair of opposing wipes which remove excess wax from the strap.

5. An apparatus as claimed in any one of claims 2 to 4, wherein said paint means is an electro-deposit means for applying a thin layer of paint on said strap, said electro-deposite including means for providing a potential difference between point and strap to attract and to apply paint to such strap, and means for wiping such painted strap prior to tower entry.

6. An apparatus as claimed in Claim 5, wherein said means for wiping comprises a pair of opposing compressible sponge pads.

7. An apparatus as claimed in Claim 5 or 6 wherein said means for providing the potential difference is adapted to vary such potential difference responsive to the strap linear speed to apply an essentially constant paint layer thickness over a wide range of strap linear speeds.

8. An apparatus as claimed in any one of Claims 2 to 7, wherein said banks of infrared emitters comprise a plurality of parallel spaced-apart high intensity shortwave infrared radiation emitting lamps mounted on ceramic bases.

9. An apparatus as claimed in Claim 8, wherein said lamps have tungsten filaments in quartz bodies and when powered, emit radiation at wavelengths of approximately .76 to 5 microns with peak energy at wavelength of approximately 1.15 microns.

10. An apparatus as claimed in Claim 9, wherein additional fan means directs blasts of air up the outside of the ceramic bases to cool the tips of the tungsten-quartz lamps.

11. An apparatus as claimed in Claim 8, Claim 9 or Claim 10, wherein said fan means directs air through ports provided in said ceramic bases into the space defined between said banks of emitters.

12. An apparatus as claimed in any one of Claims 8 to 11, wherein said controller means maintaining said banks of emitters at reduced radiation levels while the strap is stopped permits immediate response in increasing the intensity of the infrared radiation on resuming strap painting.

13. An apparatus as claimed in any one of Claims 2 to 11, wherein a plurality of spaced-apart straps are painted, comprising a slitter device for slitting a sheet of metal paid-out from a roll of sheet metal to provide said plurality of straps, said roller means at bottom and top of tower having channels provided therein to guide the straps through the tower.

14. A high speed process for painting metal strap at linear speeds as high as in the range of 1,000 feet (28,800 centimetres) per minute comprising applying a thin layer of paint on said strap which has a thickness ranging from 10 to 50 thousanths of an inch (24to 120 thousanths of a centimetre), passing such freshly painted strap between opposing banks of electrically powered high intensity shortwave infrared radiation emitter lamps to heat with such infrared radiation such strap to temperatures which dries such paint, providing a stream of air between said banks and over such strap and exhausting such air at the end of the emitter banks, constantly measuring the linear speed of such strap, controlling the electrical power to said lamps to achieve a desired strap temperature on exiting from the emitter banks for a measured linear strap speed and immediately varying the electrical powerto said lamps to vary the intensity of said radiation in response to a measured change in such strap linear speed and when strap movement is stopped, immediately dropping the intensity of radiation to provide a reduced strap temperature to maintain in such stream of air a satisfactory strap paint coating, chilling such strap as it exites such emitter banks and coiling the painted strap.

15. A high speed process according to Claim 14, wherein such strap is passed upwardly from said paint means between opposing vertically extending emitter banks.

16. A high speed process according to Claim 15, wherein such strap as it exits from said emitter banks is immediately passed over at least one polytetrafluoroethylene refrigerated roller to reduce strap temperature to a level at which such paint is tack free.

17. A high speed process according to Claim 16, wherein after passing such strap over said cooling rollers, the strap is returned downwardly to enter a refrigerated bath to reduce further the strap temperature preparatory to waxing such strap, the process comprising applying to the so-cooled strap a layer of wax and passing on the treated strap for coiling.

18. A high speed process according to any one of claims 14 to 17, wherein the paint is electrodeposited on the strap, potential difference between the charge of the paint and the strap in an electrodeposition tank is varied according to strap linear speed so as to apply to such strap a substantially constant layer thickness over a wide range of strap linear speeds.

19. A high speed process according to Claim 18, wherein the strap moves at high linear speeds and wherein prior to passing such strap upwardly between said emitter banks, both sides of the strap are wiped to remove excess water from the strap.

20. A high speed process according to any one of Claims 14 to 19, wherein high intensity shortwave infrared radiation emitter lamps are used.

21. A high speed process according to Claim 20, wherein a flow of air is directed over the tips of said lamps to cool same.

22. A high speed process according to any one of claims 14to 20, wherein a plurality of spaced-apart straps are painted.

23. Apparatus for high speed painting of metal strap substantially as herein before described with reference to the accompanying drawings.

24. A high speed process for painting metal strap substantially as hereinbefore described with reference to the accompanying drawings.